With all wheels on the ground it may not generate enough lift because of the angle of incidence.
Rotate to an angle of attack that will generate lift.
By the way, in large jets Vr and Vlo (lift off) are noticeably different.
https://www.boeing.com/commercial/aeromagazine/articles/qtr_02_09/pdfs/AERO_Q209_article04.pdf
Here is a decent example:
Last edited by B2N2; 1st Nov 2020 at 11:42.